J. M. Moran

Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, United States

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Publications (309)1115.21 Total impact

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    ABSTRACT: We report results from 1.3 mm VLBI observations of AGN jets with the Event Horizon Telescope focusing on the southern blazar 1921-293. We show the first 1.3 mm VLBI model image of 1921-293 using closure phase techniques obtained with four telescopes at three observatories: the James Clerk Maxwell Telescope (JCMT) on Mauna Kea in Hawaii, the Arizona Radio Observatory's Submillimeter Telescope (SMT) in Arizona, and two telescopes of the Combined Array for Research in Millimeterwave Astronomy (CARMA) in California in April 2009. With the greatly improved resolution compared with previous observations and robust closure phase measurement, the inner jet structure of 1921-293 was spatially resolved. The inner jet extends to the northwest along a position angle of -53° degree at a distance of 0.38 mas from the tentatively identified core, in agreement with the inner jet structure inferred from lower frequencies, and making a position angle difference of ~80° with respect to the cm-jet. The size of the compact core is 0.15 pc with a brightness temperature of 1.2 ×1011 K. Compared with those measured at lower frequencies, the low brightness temperature may argue in favor of the decelerating jet model or particle-cascade models. Some results for another blazar 3C 279 will also be presented.
    01/2013;
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    ABSTRACT: We report the first detections of circularly polarized emission at submillimeter wavelengths from the compact radio source and supermassive black hole candidate Sgr A* at a level of 1.2% ± 0.3% at 1.3 mm wavelength (230 GHz) and 1.6% ± 0.3% at 860 μm (345 GHz) with the same handedness, left circular polarization (LCP), as observed at all lower frequencies (1.4-15 GHz). The observations, taken with the Submillimeter Array in multiple epochs, also show simultaneous linear polarization (LP) at both wavelengths of about 6%. These properties differ sharply from those at wavelengths longer than 1 cm (frequencies below 30 GHz), where weak circular polarization (CP) (~0.5%) dominates over LP, which is not detected at similar fractional limits. We describe an extensive set of tests to ensure the accuracy of our measurements. We find no CP in any other source, including the bright quasar 1924-292, which traces the same path on the sky as Sgr A* and therefore should be subject to identical systematic errors originating in the instrument frame. Since a relativistic synchrotron plasma is expected to produce little CP, the observed CP is probably generated close to the event horizon by the Faraday conversion process. We use a simple approximation to show that the phase shift associated with Faraday conversion can be nearly independent of frequency, a sufficient condition to make the handedness of CP independent of frequency. Because the size of the τ = 1 surface changes by more than an order of magnitude between 1.4 and 345 GHz, the magnetic field must be coherent over such scales to consistently produce LCP. To improve our understanding of the environment of SgrA* critical future measurements includes determining whether the Faraday rotation deviates from a λ2 dependence in wavelength and whether the circular and linear components of the flux density are correlated.
    The Astrophysical Journal 01/2012; 745(2):115. · 6.73 Impact Factor
  • Diego Munoz, D. Marrone, J. Moran
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    ABSTRACT: We report the detection of circularly polarized (CP) emission from the compact radio source Sagittarius A* at a level of 1.5% at a frequency of 235 GHz (1.4 mm). Sgr A* is associated with the supermassive black hole (SMBH) in the Galactic Center. The observations, taken with the Submillimeter Array (SMA) on 03/31/2007, also show a linearly polarized (LP) component of 7%. The snr of our detection of CP is about 14. Before our measurements, CP had only been detected at frequencies between 1.4 and 15 GHz (21 and 2 cm) at levels
    05/2009;
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    E. Bloemhof, J. M. Moran, and M. J. Reid
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    ABSTRACT: Intrinsic morphologies of interstellar OH maser-emitting gas condensations have been measured, for the first time, at two distinct epochs. The shapes and orientations of these maser condensations, in the vicinity of the ultracompact H II region W3(OH), are remarkably persistent from one epoch to the next despite significant position shifts. These observations provide the first direct evidence that the motions measured are due to actual physical movement of discrete clumps of maser-emitting matter, rather than to some sort of nonkinematic effect, such as traveling excitation phenomena or chance realignments of coherency paths through the masing gas. The kinematic assumption is crucial to astrophysical applications of maser proper-motion measurements, including distance determinations and studies of source dynamics. The shapes of the OH maser spots in W3(OH) show a tendency to be elongated in a direction parallel to the shock front delineated by radio continuum maps of the H II region, supporting the picture in which masers are formed in compressed gas behind the shock front.
    The Astrophysical Journal 01/2009; 467(2):L117. · 6.73 Impact Factor
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    ABSTRACT: We present the results of the VLA and SMA continuum and emission line observations towards the massive star formation region IRAS 16547-4247. We discuss the rotating structures and the outflow observed in radio continuum and molecular tracers. We estimate the mass of the central object and discuss the nature of other sources in the region.
    01/2009;
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    ABSTRACT: Energetic flares are observed in the Galactic supermassive black hole Sagittarius A* from radio to X-ray wavelengths. On a few occasions, simultaneous flares have been detected in IR and X-ray observations, but clear counterparts at longer wavelengths have not been seen. We present a flare observed over several hours on 2006 July 17 with the Chandra X-Ray Observatory, the Keck II telescope, the Caltech Submillimeter Observatory, and the Submillimeter Array. All telescopes observed strong flare events, but the submillimeter peak is found to occur nearly 100 minutes after the X-ray peak. Submillimeter polarization data show linear polarization in the excess flare emission, increasing from 9% to 17% as the flare passes through its peak, consistent with a transition from optically thick to thin synchrotron emission. The temporal and spectral behavior of the flare require that the energetic electrons responsible for the emission cool faster than expected from their radiative output. This is consistent with adiabatic cooling in an expanding emission region, with X-rays produced through self-Compton scattering, although not consistent with the simplest model of such expansion. We also present a submillimeter flare that followed a bright IR flare on 2005 July 31. Compared to 2006, this event had a larger peak IR flux and similar submillimeter flux, but it lacked measurable X-ray emission. It also showed a shorter delay between the IR and submillimeter peaks. Based on these events we propose a synchrotron and self-Compton model to relate the submillimeter lag and the variable IR/X-ray luminosity ratio.
    The Astrophysical Journal 12/2008; · 6.73 Impact Factor
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    ABSTRACT: We present imaging observations of the evolved star IRC +10216 in the CS J = 14-13 line at 685.4 GHz and the associated submillimeter continuum at ~2'' resolution made with the partially constructed Submillimeter Array. The CS J = 14-13 line emission from the stellar envelope is well resolved both spatially and spectrally. The strong central concentration of the line emission provides direct evidence that CS is a parent molecule that forms close to the stellar photosphere, in accord with previous images of the lower excitation CS J = 2-1 line and inferences from unresolved observations of vibrationally excited transitions. The continuum emission is dominated by a compact, unresolved component, consistent with the photospheric emission, that accounts for ~20% of the broadband 450 μm flux. These are the first interferometer imaging observations made in the semitransparent 450 μm atmospheric window.
    The Astrophysical Journal 12/2008; 616(1):L51. · 6.73 Impact Factor
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    ABSTRACT: We report the discovery of H2O maser emission at 1.35 cm wavelength in seven active galactic nuclei (at distances of up to 80 Mpc) during a survey conducted at the 70 m diameter antenna of the NASA Deep Space Network near Canberra, Australia. The detection rate was ~4%. Two of the maser sources are particularly interesting because they display satellite high-velocity emission lines, which are a signature of emission from the accretion disks of supermassive black holes when seen edge-on. Three of the masers are coincident, to within uncertainties of 02, with continuum emission sources that we observed at about λ = 1.3 cm. We also report the discovery of new spectral features in the Circinus galaxy H2O maser that broaden the known velocity range of emission therein by a factor of ~1.7. If the new spectral features originate in the Circinus accretion disk, then molecular material must survive at radii ~3 times smaller than had been believed previously (~0.03 pc or ~2 × 105 Schwarzschild radii).
    The Astrophysical Journal 12/2008; 582(1):L11. · 6.73 Impact Factor
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    ABSTRACT: We present the first 865 μm continuum image with subarcsecond resolution obtained with the Submillimeter Array. These data resolve the Orion KL region into the hot core, the nearby radio source I, the submillimeter counterpart to the infrared source n (radio source L), and new submillimeter continuum sources. The radio to submillimeter emission from source I can be modeled as either the result of proton-electron free-free emission that is optically thick to ~100 GHz plus dust emission that accounts for the majority of the submillimeter flux, or H- free-free emission that gives rise to a power-law spectrum with a power-law index of ~1.6. The latter model would indicate similar physical conditions as found in the inner circumstellar environment of Mira variable stars. Future subarcsecond resolution observations at shorter submillimeter wavelengths should easily discriminate between these two possibilities. The submillimeter continuum emission toward source n can be interpreted in the framework of emission from an accretion disk.
    The Astrophysical Journal 12/2008; 616(1):L31. · 6.73 Impact Factor
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    ABSTRACT: We present the first submillimeter (865 μm) imaging spectral line survey at 1'' resolution conducted with the Submillimeter Array toward Orion KL. Within the 2 × 2 GHz bandpasses (lower and upper sidebands, 337.2-339.2 and 347.2-349.2 GHz), we find about 145 spectral lines from 13 species, six isotopologues, and five vibrational excited states. Most nitrogen-bearing molecules are strong toward the hot core, whereas the oxygen-bearing molecules peak toward the southwest in the so-called compact ridge. Imaging of spectral lines is shown to be an additional tool to improve the identifications of molecular lines. Arcsecond spatial resolution allows us to distinguish the molecular line emission of the sources I and n from that of the hot core. The only molecular species detected strongly toward source I is SiO, delineating mainly the collimated northeast-southwest low-velocity outflow. The two positions close to source I, which have previously been reported to show maser emission in the v = 0 28SiO (1-0) and (2-1) lines, show no detectable maser emission in the v = 0 28SiO (8-7) line at our spatial resolution. SiO is weak toward source n, and thus source n may not currently be driving a molecular outflow. CH3OH is the molecule with the highest number of identified lines (46) in this spectral window. This "line forest" allows us to estimate temperatures in the region, and we find temperatures between 50 and 350 K, with the peak temperatures occurring toward the hot core. The detection of strong vibrational excited line emission from the submillimeter continuum peak SMA1 supports the interpretation that the source SMA1 is likely of protostellar nature.
    The Astrophysical Journal 12/2008; 632(1):355. · 6.73 Impact Factor
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    ABSTRACT: We report the discovery of water maser emission in eight active galactic nuclei (AGNs) with the 70 m NASA Deep Space Network (DSN) antennas at Tidbinbilla, Australia, and Robledo, Spain. The positions of the newly discovered masers, measured with the VLA, are consistent with the optical positions of the host nuclei to within 1 σ (03 radio and 13 optical) and most likely mark the locations of the embedded central engines. The spectra of two sources, NGC 3393 and NGC 5495, display the characteristic spectral signature of emission from an edge-on accretion disk, with orbital velocities of ~600 and ~400 km s-1, respectively. In a survey with DSN facilities of 630 AGNs selected from the NASA Extragalactic Database, we have discovered a total of 15 water maser sources. The resulting incidence rate of maser emission among nearby (vsys < 7000 km s-1) Seyfert 1.8-2.0 and LINER systems is ~10% for a typical rms noise level of ~14 mJy over 1.3 km s-1 spectral channels. As a result of this work, the number of nearby AGNs (vsys < 7000 km s-1) observed with <20 mJy rms noise has increased from 130 to 449.
    The Astrophysical Journal 12/2008; 638(1):100. · 6.73 Impact Factor
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    ABSTRACT: Using data from a seven-telescope VLBI experiment, we have remapped the 1665-MHz OH maser emission from W3(OH), a site of current star formation roughly 2.2 kpc distant. Both circular polarizations were observed with excellent UV coverage, and the resolution of the synthesized maps is about 5 milli-arc seconds. By comparing our new maps (epoch 1986) with maps made at an earlier epoch (1978), we can measure proper motions of individual maser features. Since the maser features are distributed in projection against the ultra-compact HII region, a study of their proper motions can probe the kinematics in the immediate vicinity of this very young object. Our preliminary results indicate a significant ordered divergent motion.
    05/2008: pages 228-230;
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    ABSTRACT: We present results from two multiwavelength monitoring campaigns that were performed on Sgr A* using Chandra, Keck II, SMA, and CSO. These campaigns have, for the first time, successfully observed two flares simultaneously in the X-ray, NIR, and submillimeter. One flare was observed on 2005 July 31 (UT); the other was observed on 2006 July 17 (UT). Observations with the Keck II AO system at K' and L' showed that both flares appeared to be of similar amplitudes and spectral indices as previously observed NIR flares, although the Keck observations missed the peak of the 2006 flare by about 30 minutes. The submillimeter flares were likewise of similar amplitudes, about 1 Jy. However, the submillimeter peak of the 2006 flare lagged the shorter wavelengths by nearly 100 minutes, while the lag of the submillimeter peak in 2005 apears to have been about 80 minutes shorter. Remarkably, the 2006 flare shows a strong X-ray flare, while the 2005 flare has no detectable X-ray emission above the constant level produced by diffuse gas in the central parsec. Thus, the two flares have remarkably different X-ray to NIR flux ratios and submillimeter lags. We have found a possible correlation between the X-ray to NIR flux ratio and the time lag of the submm peak in the two flares that can be explained with an adiabatically expanding relativistic plasma model.
    05/2008;
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    ABSTRACT: Channel data for BM056C in Table 5 should be corrected as follows:NSoffcorrected=NSofftable-66.0(nu-22.19856/22.19856), wherenu=22.23508(1-RelVel/c/1+RelVel/c)1/2 and c is the speed of light, i.e., 2.99792458×105 km s-1. The subscripts ``corrected'' and ``table'' refer to the corrected and table values, respectively. Nomenclature and units follow those of the published table. This correction applies to data lines 1-1876, 1885-1895, 1901-1903, 1907-1909, and 1912-1935 only. A corrected version of the print stub table and link to a corrected version of the full, machine-readable data table are given below.
    The Astrophysical Journal 01/2008; 673:1249-1249. · 6.73 Impact Factor
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    ABSTRACT: We present VLA 1.3 cm radio continuum and water maser observationsas well as SMA SO2 (226.300 GHz) and dust continuum observationstoward the massive star formation region IRAS 16547-4247. We foundevidence of a rotating structure around a central massive source at small scale ( 10 AU) traced by the water masers and at large scale( 1000 AU) traced by molecular line emission. The two structures areconsistent with each other in the sense of rotation and inclinationangle. The position angle of the rotating structures is roughlyperpendicular to the overall outflow observed in radio continuum andmolecular tracers. We estimate the mass of the central source to bearound 14 solar masses from the water masers and the SO2 emission which trace quite different size scales. We also observed water masers that are associated with the large scale molecular outflowfrom the system. In addition we have detected maser emission that isprobably associated with other sources in the region.
    12/2007;
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    ABSTRACT: A major issue for understanding the accretion process of AGN is determining the structure of the inner accretion disk. The only way to map the disk at distances < 1 pc from the central supermassive black hole is by using radio interferometric observations of nuclear water masers. In a new study of the nuclear masers of nearby Seyfert 2/LINER NGC 4258, we have imaged a sub-parsec (0.11 -- 0.28 pc) portion of the disk at 18 epochs using VLBI. The observations have enabled a first measurement of the thickness of the maser medium to be 5 muas or 0.0002 pc (1sigma). Assuming that this corresponds to the thickness of the accretion disk, hydrostatic equilibrium requires a gas temperature of &ap; 600 K i.e., consistent with the physical conditions required to pump the masers. We confirm that warping of the disk could result in obscuration of the central engine, and that there is a characteristic radial scale of 0.027 pc for maser emission along the disk midline (the diameter perpendicular to the line-of-sight to the black hole) consistent with a model of spiral density waves in the disk. We find a trend in centripetal accelerations of masers in the line-of-sight to the black hole, as a function of disk impact parameter, that is long-lived with respect to the transit time of masers orbiting in front of the black hole. The trend could be due to (i) a spiral arm of mass 105 M&sun; of pattern speed
    12/2007;
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    ABSTRACT: We have placed an upper limit on the magnitude of the rotation measure of 7 × 10^5 rad m-2 for the putative Faraday screen (magnetized plasma) in front of Sgr A*, the radio source associated with the black hole in the Galactic Center. There is evidence that the actual rotation measure is about -5 ×105 rad m-2. With a simple model of equipartition of energy and reasonable inner radius for the screen, the accretion rate is estimated to be less than 10-6M⊙yr-1. In addition, we have detected, for the first time, intra-day variability in the polarization of Sgr A*, which may be due to either intrinsic variations in Sgr A* or variations in the composition of the Faraday screen.
    10/2007: pages 163-169;
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    ABSTRACT: We report measurements of centripetal accelerations of maser spectral components of NGC 4258 for 51 epochs spanning 1994 to 2004. This is the second paper of a series, in which the goal is determination of a new geometric maser distance to NGC 4258 accurate to possibly ~3%. We measure accelerations using a formal analysis method that involves simultaneous decomposition of maser spectra for all epochs into multiple, Gaussian components. Components are coupled between epochs by linear drifts (accelerations) from their centroid velocities at a reference epoch. For high-velocity emission, accelerations lie in the range -0.7 to +0.7 km/s/yr indicating an origin within 13 degrees of the disk midline (the perpendicular to the line-of-sight to the black hole). Comparison of high-velocity emission projected positions in VLBI images, with those derived from acceleration data, provides evidence that masers trace real gas dynamics. High-velocity emission accelerations do not support a model of trailing shocks associated with spiral arms in the disk. However, we find strengthened evidence for spatial periodicity in high-velocity emission, of wavelength 0.75 mas. This supports suggestions of spiral structure due to density waves in the nuclear accretion disk of an active galaxy. Accelerations of low-velocity (systemic) emission lie in the range 7.7 to 8.9 km/s/yr, consistent with emission originating from a concavity where the thin, warped disk is tangent to the line-of-sight. A trend in accelerations of low-velocity emission as a function of Doppler velocity may be associated with disk geometry and orientation, or with the presence of spiral structure. Comment: Accepted to ApJ, 48 pages and 20 figures
    The Astrophysical Journal 09/2007; · 6.73 Impact Factor
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    ABSTRACT: We report a three year, 18 epoch, VLBI monitoring study of H2O masers in the sub-parsec, warped, accretion disk within the NGC4258 AGN. Our immediate goals are to trace the geometry of the underlying disk, track rotation via measurement of proper motion, and ascertain the radii of masers for which centripetal acceleration may be measured separately. The monitoring includes ~ 4 times as many epochs, ~ 3 times denser sampling, and tighter control over sources of systematic error than earlier VLBI investigations. Coverage of a ~ 2400 km/s bandwidth has also enabled mapping of molecular material ~ 30% closer to the black hole than accomplished previously, which will strengthen geometric and dynamical disk models. Through repeated observation we have also measured for the first time a 5 microarsecond (1 sigma) thickness of the maser medium. Assuming this corresponds to the thickness of the accretion disk, hydrostatic equilibrium requires a disk plane temperature of ~ 600 K. Our long-term goal is a geometric distance to NGC4258 that is accurate to ~ 3%, a ~ 2 times improvement over the current best estimate. A geometric estimate of distance can be compared to distances obtained from analysis of Cepheid light curves, with the intent to recalibrate the extragalactic distance scale with reduced systematic uncertainties. This is the first paper in a series. We present here VLBI observations, data reduction, and temporal and spatial characteristics of the maser emission. Later papers will report estimation of orbital acceleration and proper motion, modeling of disk 3-D geometry and dynamics, and estimation of a "maser distance." Estimation of a "Cepheid distance" is presented in a parallel paper series.
    The Astrophysical Journal 01/2007; 659. · 6.73 Impact Factor
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    ABSTRACT: Aims.We present molecular line observations of the molecular core associated with IRAS 16547-4247, which have allowed us to determine its physical and kinematical properties at angular resolutions of ~18´´.Methods.The observations were made using the Atacama Pathfinder Experiment Telescope in the $J = 3 \rightarrow 2$ transitions of $^{12}$CO and $^{13}$CO, $J = 4 \rightarrow 3$ transitions of HCO$^+$ and H$^{13}$CO$^+$, and $J = 7 \rightarrow 6$ transition of CS.Results.Our observations reveal the presence of a collimated bipolar outflow with lobes ~0.7 pc in extent and aligned with the thermal jet located at the center of the core. The morphology and velocity structure of the flow are well described by a biconical outflow that is inclined from the line of sight by an angle of 84°, has a semi-opening angle of 14$^{\circ}$, and in which the gas moves outwards with a constant total velocity, with respect to the cone apex, of ~120 km s$^{-1}$. The outflow is massive and energetic (flow mass ~$110$ $M_{\odot}$; mass outflow rate ~$2\times10^{-2}$ $M_{\odot}$ yr$^{-1}$; momentum ~$2\times10^3$ $M_{\odot}$ km s$^{-1}$ and kinetic energy ~$9\times 10^{47}$ erg), and has a dynamical time scale of $6\times10^3$ yr. These parameters are consistent with the flow being driven by a young massive stellar object with $L_{\rm bol} \sim 6\times10^4$ $L_{\odot}$.
    Astronomy and Astrophysics 01/2007; · 5.08 Impact Factor

Publication Stats

4k Citations
1,115.21 Total Impact Points

Institutions

  • 1978–2012
    • Harvard-Smithsonian Center for Astrophysics
      • • Smithsonian Astrophysical Observatory
      • • Institute for Theory and Computation
      Cambridge, Massachusetts, United States
  • 2003
    • University of Tasmania
      • School of Mathematics & Physics
      Hobart Town, Tasmania, Australia
  • 1983–1993
    • Universidad Nacional Autónoma de México
      • Institute of Astronomy
      Ciudad de México, The Federal District, Mexico
  • 1992
    • CSU Mentor
      Long Beach, California, United States
  • 1988
    • University of California, Berkeley
      Berkeley, California, United States
  • 1977
    • California Institute of Technology
      Pasadena, California, United States
  • 1976
    • University of Toronto
      Toronto, Ontario, Canada
  • 1967–1976
    • Massachusetts Institute of Technology
      • Research Laboratory of Electronics
      Cambridge, Massachusetts, United States